Reduced head and brain size for age and disproportionately smaller thalami in child-onset MS.

OBJECTIVE: Whole brain and regional volume measurement methods were used to quantify white matter, gray matter, and deep gray matter structure volumes in a population of patients with pediatric-onset multiple sclerosis (MS). METHODS: Subjects included 38 patients (mean age 15.2 ± 2.4 years) and 33 age- and sex-matched healthy control (HC) participants. MRI measures included intracranial volume, normalized brain volume, normalized white and gray matter volume, and volumes of the thalamus, globus pallidus, putamen, and caudate. Because these volumes vary across age and sex in children, we normalized the volume measurements for MS and control groups by computing z scores using normative values obtained from healthy children enrolled in the MRI Study of Normal Brain Development. RESULTS: The intracranial volume z score was significantly lower in the patients with MS (-0.45 ± 1.16; mean ± SD) compared with the HC participants (+0.25 ± 0.98; p = 0.01). Patients with MS also demonstrated significant decreases in normalized brain volume z scores (-1.09 ± 1.49 vs -0.05 ± 1.22; p = 0.002). After correction for global brain volume, thalamic volumes in the MS population remained lower than those of HCs (-0.68 ± 1.72 vs 0.15 ± 1.35; p = 0.02), indicating an even greater loss of thalamic tissue relative to more global brain measures. Moderate correlations were found between T2-weighted lesion load and normalized thalamic volumes (r = -0.44, p < 0.01) and normalized brain volume (r = -0.47, p < 0.01) and between disease duration and normalized thalamic volume (r = -0.58, p < 0.001) and normalized brain volume (r = -0.46, p < 0.01). CONCLUSIONS: When compared with age- and sex-matched control subjects, the onset of MS during childhood is associated with a smaller overall head size, brain volume, and an even smaller thalamic volume.

A novel, 11 nucleotide variant of chi, chi*: one of a class of sequences defining the Escherichia coli recombination hotspot chi.

In wild-type Escherichia coli, recognition of the recombination hotspot, chi (5'-GCTGGTGG-3'), by the RecBCD enzyme is central to homologous recombination. However, in the recC* class of RecBCD mutants, stimulation of recombination by the canonical chi sequence is not detectable, but the levels of homologous recombination are nearly wild-type. In vivo studies demonstrate that a member of this class of mutants, the recC1004 allele, encodes an enzyme that responds to a novel variant of chi, termed chi* (5'-GCTGGTGCTCG-3'). Here, we establish that, in vitro, the chi* sequence is recognized more efficiently by the RecBC(1004)D enzyme than is the wild-type chi. This is manifest by both a greater modification of nuclease activity and a higher stimulation of RecA protein-mediated joint molecule formation at chi* than at chi. Sequencing of the recC1004 gene revealed that it contains a frameshift mutation, which results in a replacement of nine of the wild-type amino acid residues by eight in the mutant protein, and defines a locus that is important for the specificity of chi-recognition. In addition, we show that this novel, 11 nucleotide chi* sequence also regulates the wild-type RecBCD enzyme, supporting the notion that variants of the canonical chi constitute a class of sequences that regulate the recombination function of RecBCD enzyme.

Facilitated loading of RecA protein is essential to recombination by RecBCD enzyme.

Although the RecB(2109)CD enzyme retains most of the biochemical functions associated with the wild-type RecBCD enzyme, it is completely defective for genetic recombination. Here, we demonstrate that the mutant enzyme exhibits an aberrant double-stranded DNA exonuclease activity, intrinsically producing a 3'-terminal single-stranded DNA overhang that is an ideal substrate for RecA protein-promoted strand invasion. Thus, the mutant enzyme constitutively processes double-stranded DNA in the same manner as the chi-modified wild-type RecBCD enzyme. However, we further show that the RecB(2109)CD enzyme is unable to coordinate the loading of RecA protein onto the single-stranded DNA produced, and we conclude that this inability results in the recombination-defective phenotype of the recB2109 allele. Our findings argue that the facilitated loading of RecA protein by the chi-activated RecBCD enzyme is essential for RecBCD-mediated homologous recombination in vivo.

The reduced levels of chi recognition exhibited by the RecBC1004D enzyme reflect its recombination defect in vivo.

Homologous recombination in Escherichia coli is initiated by the RecBCD enzyme and is stimulated by an 8-nucleotide element known as Chi (chi). We present a detailed biochemical characterization of a mutant RecBCD enzyme, designated RecBC1004D, that displays a reduced level of chi site recognition. Initially characterized genetically as unable to respond to the chi sequence, we provide evidence to indicate that the ability of this mutant enzyme to respond to chi is reduced rather than lost; the mutant displays about 20-fold lower chi recognition than wild-type RecBCD enzyme. Although this enzyme exhibits wild-type levels of double-stranded DNA exonuclease, helicase, and ATPase activity, its ability to degrade single-stranded DNA is enhanced 2-3-fold. The data presented here suggest that the reduced recombination proficiency of the recBC1004D strain observed in vivo results from a basal level of modification of the RecBC1004D enzyme at both chi-specific, as well as nonspecific, DNA sequences.

Magnetic resonance imaging in the diagnosis of dominantly inherited cerebello-olivary atrophy: a clinicopathologic study.

To facilitate the study of cerebellar degenerative disorders, improved clinical diagnosis is needed. Cerebello-olivary atrophy is pathologically distinct, but until now its diagnosis has been thought to require postmortem examination. This condition was considered as a possible diagnosis in two patients from different families with dominantly inherited ataxia. The affected members of each family demonstrated a stereotyped, progressive, "pure" cerebellar syndrome, which began with gait ataxia followed years later by dysarthria and limb ataxia. The autopsy findings for the first patient's father revealed paleocerebellar and olivary atrophy, characteristic of cerebello-olivary atrophy. Magnetic resonance imaging (MRI) of the brain of both patients revealed medullary, vermian and, to a lesser extent, cerebellar hemispheric atrophy but a normal pons. Dominantly inherited cerebello-olivary atrophy was diagnosed in both patients. Characteristic clinical and MRI features thus permit a confident clinical diagnosis of dominantly inherited cerebello-olivary atrophy. Recognition of this entity during life should advance the classification of cerebellar degenerative disorders.

Energetics of human muscle: exercise-induced ATP depletion.

The energetics of human muscle have been investigated in vivo during and after fatiguing aerobic, dynamic exercise. Changes in cytoplasmic pH and concentrations of phosphocreatine, ATP and Pi were followed using 31P nuclear magnetic resonance spectroscopy. ATP was significantly depleted in 6 out of 12 experiments and in these 6 experiments decreased to 55 +/- 5% of the pre-exercise concentration. Depleted muscle had a lower phosphocreatine concentration (17 +/- 5% of resting value) and lower pH (6.12 +/- 0.04) than fatigued muscle in which ATP loss was not observed (26 +/- 5% for phosphocreatine and 6.37 +/- 0.09 for pH). The free energy of hydrolysis of ATP was not significantly different in the two groups and was also similar in exhausted and nonexhausted muscle. Loss of ATP was associated with altered recovery of the muscle: [phosphocreatine], [Pi], and pH returned more slowly to their pre-exercise values and the initial rate of oxidative phosphorylation was diminished. The restitution of [ATP] to its pre-exercise value was much slower than that of the other metabolites.